lightningd: add override amt to invoice_check_payment

Adds `expected_msat_override` to the `invoice_check_payment` check. If
it's set, it will be used to override the invoice amount as the expected
amount of the payment check.

This enables us to charge a different amount for a payment than the
amount stated on the invoice.

Signed-off-by: Peter Neuroth <pet.v.ne@gmail.com>

wallet/test/run-wallet.c

@@ -391,6 +391,7 @@ const struct invoice_details *invoice_check_payment(const tal_t *ctx UNNEEDED,
 						    struct lightningd *ld UNNEEDED,
 						    const struct sha256 *payment_hash UNNEEDED,
 						    const struct amount_msat msat UNNEEDED,
+						    const struct amount_msat *expected_msat_override UNNEEDED,
 						    const struct secret *payment_secret UNNEEDED,
 						    const char **err UNNEEDED)
 { fprintf(stderr, "invoice_check_payment called!\n"); abort(); }